A variety of vehicular keyless entry systems are proposed (for example, JP 2008-14019A corresponding to US 2009/0289759 A1). Each of the systems checks up a portable device and controls locking and unlocking operations of a vehicle door and starting a vehicle engine in accordance with a result of checkup.
Some of the vehicular keyless entry systems described above are capable of checking up any one of authorized portable devices as an object of checkup, so that the vehicle door may be locked or unlocked or the vehicle engine may be started by any one of the authorized portable devices.
According to the vehicular keyless entry systems, although an authorized portable device is being locked in inside a vehicle compartment, the vehicle door may inadvertently be locked by successful checkup about the other authorized portable device carried by a user.
An unauthorized third person may intrude into the vehicle compartment by shattering a windshield glass under a condition that the vehicle door is being locked by the checkup operation about the other authorized portable device carried by the user with the authorized portable device being left inside the vehicle compartment. In this instance, the checkup operation will be made successfully about the authorized portable device left in the vehicle compartment. It is thus likely that the vehicle engine will be started and the vehicle will be stolen.
It is preferred that the vehicle door is locked in performing the vehicle door locking control operation after confirming that all the authorized portable devices are outside the vehicle compartment and no other authorized portable devices are inside the vehicle compartment.
In case of a plurality of authorized portable devices, it need be specified whether each portable device is detected inside the vehicle compartment or outside the vehicle or not detected. For this purpose, the checkup operation must be performed with respect to each portable device by switching over areas of checkup operation.
If the area of checkup operation is switched over sequentially with respect to each portable device to specify the location of the portable device, it takes a long time to lock the door, thus resulting in poor response. The response gets worse as the number of authorized potable devices increases.